John Dory: Slice the medium John Dory fillets into 2 or large ones into 3. Toss the fillets in the remaining ingredients and leave to marinate in the refrigerator for 15-30 minutes.
To Cook: Heat a little olive oil in a large frying pan over a moderate high heat. Place the fillets skin side down in the hot oil and reduce the heat slightly. Cook the fillets for 3 minutes on the skin side and 2 minutes on the flesh side (the skin should be slightly crisp and the edges golden brown). Remove the fish from the heat and serve or keep warm until ready to serve.
Baby Spinach and Rocket Salad: Toss all the ingredients together gently when ready to serve (don't prepare in advance as the leaves will wilt).
To Serve: Place 2 polenta croutons on each plate and a generous serving of salad. Arrange the John Dory fillets on the croutons. Serve.